By the procedure previously described for the isolation of ovine beta-LPH and ACTH, 3.5 mg beta t-LPH and 10 mg alpha t-ACTH were isolated to homogeneity from 3,000 fresh turkey pituitaries. Primary structure of beta t-LPH has partially been determined. Because of limited amount of beta t-LPH, it is not possible to elucidate the complete amino acid sequence of beta t-LPH. However, it appears that the COOH-terminal 31 amino acids (-endorphin segment) are comparatively conserved during evolution. When amino acid sequences of turkey and ostrich ACTHs are compared, the NH2-terminal 26 amino acid residues are nearly identical except that residue in position 16 is Arg instead of Lys, 17 Lys instead of Arg and 20 Ile instead of Val. When compared with the ovine hormone, most of the differences are located at the COOH-terminal portion of the molecule. It is known that biological activity of ACTH resides in the NH2-terminal region of the hormone. The variability in the sequence of COOH-terminal residues in various ACTHs is not surprising. The three peptides (Ava2, Cys5-Cys10)-ACTH-(2-19) (I), (Ava2, Cys3-Cys10)-ACTH-(2-19) (II), and (Gly1, Cys2-Cys10)-ACTH-(1-19) (III) were synthesized by the solid-phase method. The synthetic peptides were assayed for in vitro steroidogenic activity and in vitro lipolytic activity against (Ava2-)-ACTH-(2-19) standard. It was found that all of the peptides have reduced biological activity; however, some differences between the peptides may be noted. Peptide I has a greater in vitro steroidogenic potency than peptides II and III, but the nonparallelism between the dose-response curves of peptides II and III and (Ava2)-ACTH-(2-19) prevented an accurate estimate of relative potencies. A comparable result was obtained for lipolytic assay in rabbit fat cells, but there was less distinction between peptides in this assay than there was in the steroidogenic assay or lipolytic assay in rat fat cells.